LONDON -- The River Thames continued to rise in parts of Western England Monday as the worst flooding since the 1940s forced evacuations and cut power.

Days of rain that is forecast to continue through this week have caused the Thames and Severn rivers to spill over their banks, causing heavy damage throughout the counties of Worcestershire, Warwickshire and Gloucestershire, Sky News reported.

Forecasters said they expected the rivers to crest at midweek. Flood warnings for Oxfordshire, Bedfordshire and the Midlands warned that some rivers could top out at 20 feet over flood stage, the BBC said.

British Prime Minister Gordon Brown flew over the area by helicopter to assess the situation as insurers said early estimates of damage could surpass $2 billion.

In Gloucestershire, the military shipped 600 water tanks into the area while 22 miles of temporary water mains are erected to pump fresh water from outside the county.

Police in Worcestershire said thieves had been stealing from abandoned and storekeepers across the region reported waves of panic buying, the report said.